(1) Field of the Invention
This invention relates to chairs; and, more particularly, to chairs having two parts relatively movable with respect to each other.
(2) Prior Art
A secretarial posture chair generally includes a back rest portion secured to the seat and legs of the chair by a vertically oriented upright post. The back rest portion of such chairs is dimensioned so as to support the small of the back of a person sitting in the chair. In order to permit the chair to be usable by different persons, the back rests of such posture chairs are typically vertically adjustable. In some prior art chairs, the back rest is mounted so as to pivot along its horizontal axis relative to the vertical support post. As a result, the back rest can be vertically adjusted to fit different people using the chair, and the back rest can pivot so the top edge of the back rest does not uncomfortably impinge on the user's back.
Chairs are known employing an external, clearly visible mechanism which permits limited pivotal movement along the horizontal axis of the back rest. Such a mechanism is unsightly and does not adapt to modern furniture design. Later versions of such posture chairs include enclosed, adjusting mechanisms with the capability of limited horizontal pivotal movement. An example of such an arrangement is found in U.S. Pat. No. 4,043,592 to Bernard J. Fries entitled ADJUSTABLE SEAT BACK MECHANISM, issued Aug. 23, 1977. The patent teaches an embodiment wherein a housing slidably mounted on the vertical post is secured to a back rest support plate by a pair of bolts which pass through a pair of resilient blocks. Compression of the resilient blocks permits pivoting of the housing relative to the support plate. In another embodiment, a spring assembly including a spring support plate and a leaf spring is disposed between the housing and the support plate. A pivot pin then passes transversely through the support plate, the spring support plate, and the housing to pivotally interconnect the elements.
The use of a pair of resilient blocks is disadvantageous because each block must be separately mounted and properly aligned with both the vertical support and the pivoting back member so that both of the two members properly engage the resilient blocks. The use of a spring is disadvantageous because the spring typically is expensive. Further, metal springs may cause excessive and rapid wear of engaging parts and produce an undesirable rubbing or squeaking noise. As a result, while rubber blocks may be relatively inexpensive they are difficult to install and position properly; and, fabricating a spring and installing it produces an undesirable large expense. It is particularly significant to appreciate that when a great number of chairs are made, even a small saving in cost of one part in a chair can result in a substantial total saving and that even a small improvement in the ease of fabrication can result in the substantial overall improvement in fabrication.